update hierarchical IIIF collection creation to use PUT and POST

[JackLewis-digirati]

Currently, collections work like the following:

POST /collection1/collectionChild
{
  "@context":  "standard iiif context",
   "(my vanilla collection)"
}

but it needs to work like this on the hierarchical URL:

/// slug is explicitly provided but requires non-standard property
// TODO - Disallow this? Only vanilla IIIF on hierarchical URLs?
POST /collection1/
{
  "@context":  [
        "standard iiif context",
        "dlcs context
   ],
   "(my not completely vanilla collection)"
   "slug": "collectionChild"
}

// recognise id as one of our own, slug is implied by last path element of id
POST /collection1/
{
  "id": "https://dlc.services/iiif/collection1/collectionChild,
  "@context":  "standard iiif context",
   "(my vanilla collection)"
}

// recognise id is not one of ours, but what's the slug?
400 Bad Request - you need to do a PUT to get this one in because we can't work out what the slug should be
POST /collection1/
{
  "id": "https://bl.uk/gary-collection",
  "@context":  "standard iiif context",
   "(my vanilla completely external collection)"
}

// (no id, or ignore id) - don't need it
PUT /collection1/collectionChild
{
  "@context": "standard iiif context",
   "(my vanilla collection)"
} 

// This is fine, parent and slug defined by PUT URL
PUT /collection1/collectionChild
{
  "id": "https://bl.uk/gary-collection",
  "@context":  "standard iiif context",
   "(my vanilla completely external collection)"
} 

• Any id property on the resource supplied in either PUT or POST is ignored - the URL PUT to, or the URL POSTed to + slug, tells us what the id will be in the hierarchy.

https://deploy-preview-2--dlcs-docs.netlify.app/api-doc/iiif#example-create-a-iiif-collection-within-a-storage-collectionhierarchical